FIG. 1a shows a conventional magnetic disk drive. The disk drive includes a magnetic disk 1 for storing data, and a read-write head 2 for reading data from and writing data to magnetic disk 1. Typically, read-write head 2 comprises a slider upon which a transducer is mounted. During use, disk 1 is rotated by a motor (not shown). Rotation of disk 1 generates wind which causes read-write head 2 to "fly" above the disk surface. Disk drives of this nature are used extensively.
Read-write head 2 is mounted on an actuator arm 3, which in turn can be rotated by a motor 4 so that read-write head 2 can be maneuvered over and read data from the various tracks of disk 1. Actuator arm 3 holds read-write head 2 at an angle known as the "skew angle." The skew angle is defined as the angle (shown in FIG. 1a as .theta.) between the longitudinal axis of read-write head 2 (which is parallel to actuator arm 3) and the wind direction W at the location where read-write head 2 is flying. Skew changes as read-write head 2 is moved by actuator arm 3 from the inner diameter to the outer diameter of disk 1 as shown in FIG. 1a.
A class of sliders that perform well are negative pressure air bearing (NPAB) sliders. Strom et al., U.S. Pat. No. 5,062,017 (incorporated herein by reference) discloses a NPAB slider which includes a cross-rail extending between first and second side rails. A similar NPAB slider 110 is shown in FIG. 2. Slider 110 comprises a leading edge 100, a trailing edge 101, first and second side edges 102, 103, first and second raised side rails 104, 105 positioned along first and second side edges 102, 103, respectively, and a leading bridge or cross rail 106. During use, cross-rail 106 creates negative pressure in a region 107. Slider 110 also includes leading edge tapers 108, 109 for facilitating flow of air under rails 104, 105 during takeoff.
NPAB slider 110 is formed using a two step etch process. Negative pressure region 107 is etched to a first depth, typically 5 to 10 microns (.mu.m) below the surfaces of first and second raised side rails 104, 105. Cross-rail 106 is etched to a second depth, typically 1 to 2 .mu.m below the surfaces of first and second raised side rails 104, 105.
Standard slider dimensions are 4.0 mm.times.3.2 mm.times.0.85 mm (length, width, height). However the art is moving towards smaller sliders, such as nano and pico sliders. Standard slider dimensions are reduced by 50% in nano sliders, and by 70% in pico sliders. As shown by the dimensions in FIG. 2, slider 110 is a nano slider.
Slider performance is measured using several parameters. One important parameter is the "fly height", which is the distance between the magnetic transducer on read-write head 2 and the magnetic layer in disk 1. (FIG. 1a).
Another important parameter is "roll". Roll is the difference between the distance between inside rail 104 and disk 1 and the distance between outside rail 105 and disk 1 while read-write head 2 is flying over disk 1.
Another important parameter is "pitch". Pitch is the difference between the distance between leading edge 100 and disk 1 and the distance between trailing edge 101 and disk 1 while read-write head 2 is flying over disk 1.
In magnetic recording technology, there are two areas of desired continual improvements. The first is to increase the recording density to maximize the amount of data that can be stored on the surface of a disk. The second is to reduce the time in which data stored on a disk is accessed, i.e. to reduce the access time.
Recording density can be increased by reducing the average fly height over the entire surface of the disk. The average fly height must be sufficient to prevent contact between the slider and the disk due to fly height non-uniformity across the disk surface. Fly height non-uniformity results in large part from variations in wind speed and skew. Thus sliders with designs which are relatively insensitive to wind speed variation and skew variation have better fly height uniformity over the entire disk surface. As fly height uniformity is improved, the average fly height can be reduced, thus allowing the recording density to be increased.
Of importance, NPAB sliders improve fly height uniformity across the disk surface by offsetting changes in lift related to changes in wind speed. Referring to FIG. 2, the positive pressure exerted on the first and second raised side rails 104, 105 provides lift, or upward force on slider 110. The total downward force on slider 110 is the sum of the force caused by negative pressure generated in region 107 and a fixed external load (not shown) applied on slider 110 by the head suspension, known as suspension preload. As the disk rotates, the wind speed beneath the slider is greater at the outer diameter OD of the disk than at the inner diameter ID (FIG. 1a). Thus the lift is greater at outer diameter OD than at inner diameter ID. However, more negative pressure is also generated at the outer diameter OD of the disk which offsets the increase in lift due to greater wind speed. Thus, negative pressure designs improve fly height uniformity.
Fly height uniformity is also improved by reducing slider skew sensitivity. At skewed conditions, the effective areas of first and second raised side rails 104, 105 decrease (see Strom et al., '017, column 2, lines 19-46). This decrease in effective area results in decreased lift and fly height. Thus skew creates fly height non-uniformity. Therefore sliders with reduced skew sensitivity have improved fly height uniformity.
Fly height uniformity is further improved by reducing roll associated with skew. At skewed conditions, NPAB sliders exhibit roll because downstream rail 105 (or 104 depending upon whether the skew angle is negative or positive) receives little air from negative pressure region 107 while at the same time upstream rail 104 (or 105) receives air at ambient pressure. Since the magnetic transducer is typically located at trailing edge 101 of outer rail 105, roll affects transducer performance because it introduces fly height non-uniformity. Again, sliders with reduced skew sensitivity have improved fly height uniformity.
It is possible to reduce fly height by selecting an appropriate pitch angle. Sliders with large pitch exhibit reduced stiffness about the pitch axis, and thus have a tendency to rock about the pitch axis when dynamically excited (e.g. if the slider hits an asperity on the disk). The slider must fly at a height which is high enough to accommodate such rocking motion. As pitch is reduced, the dynamic performance of the slider is improved, and the tendency of the slider to rock is reduced. Thus, sliders with reduced pitch may be used with a lower fly height. However, there are disadvantages to having pitch that is too low. For example, if pitch is too low, it becomes more likely that the head will strike asperities on the disk, thereby increasing the likelihood of mechanical failure. Accordingly, read-write heads should have pitch angles that are neither too large nor too small.
Recording density can also be improved by reducing slider sensitivity to various manufacturing processes used in the production of sliders. In particular, recording density can be improved by reducing slider sensitivity to taper length variations caused during manufacturing. Taper length variations change the surface areas of leading edge tapers 108, 109 and thus the lift provided by leading edge tapers 108, 109. Also, taper length variations change the surface areas of first and second raised side rails 104, 105 and thus the lift provided by first and second raised side rails 104, 105. The combined effect changes the overall lift on slider 110. As the overall lift varies, so does the fly height. Thus the average fly height must be increased to account for taper length variations caused during manufacturing. As discussed, increasing the average fly height reduces recording density.
Reducing access time is the second area of continual desired improvement in magnetic recording technology. Referring to FIG. 1a, during accessing, read-write head 2 is moved sideways (see arrow A) from one data track to another by actuator arm 3. This is known as "head seek". By reducing the amount of time required to move from one track to another, access time is reduced. One way to reduce the amount of time required to move read-write head 2 from one track to another is to increase the speed at which read-write head 2 moves from one track to another, i.e. the access velocity.
Increasing access velocity increases access skew (skew created momentarily by the sideways motion of the slider during accessing). FIG. 1b is a vector diagram of a slider during accessing at the inner diameter of disk 1 (FIG. 1a). Referring to FIG. 1b, access skew (.theta..sub.A) is related to skew angle .theta., access velocity (V.sub.A) and the velocity of the disk surface where the slider is flying, i.e. disk velocity (V.sub.D), as set forth in the following equation: ##EQU1##
As set forth in equation 1, at a fixed disk velocity V.sub.D, increasing access velocity V.sub.A increases access skew .theta..sub.A. Access skew adversely affects fly height uniformity for the same reasons as those discussed above for skew. However, it is desirable to maintain a constant fly height during accessing. Therefore, sliders with reduced skew sensitivity, hence improved fly height uniformity during accessing, exhibit superior accessing performance.
It is desirable to increase recording density and accessing performance. Thus it is desirable to design a slider with reduced sensitivities to wind speed and skew. It is also desirable to design a slider with reduced sensitivity to taper length variation and to simplify manufacturing by producing a NPAB slider using only a single etch step.
It is also important to be able to readily tailor the roll, pitch and fly height characteristics to meet specifications established for different disk drives by their manufacturers. These characteristics can be tailored by controlling the magnitude and distribution of the force created by negative pressure as part of the overall NPAB slider design. Therefore, it is desirable to have structures in the NPAB slider that provide an easy means of controlling the magnitude and distribution of the force created by negative pressure.